Copper-Catalyzed Cross-Nucleophile Coupling of Organoboranes

Metal-catalyzed cross-coupling reactions are an essential tool for carbon-carbon bond formation and generally involve one electrophilic and one nucleophilic coupling partner. In the wake of these traditional cross-coupling reactions, cross-electrophile coupling has emerged as a powerful complementary approach for joining two electrophilic components. The third general strategy, cross coupling of two nucleophiles, remains largely underdeveloped. Here we report a cross-nucleophile coupling of alkenylboronic esters and alkylboranes using a copper catalyst and acetophenone as the terminal oxidant. The reaction tolerates a range of functional groups and provides access to 1,2- and 1,1-disubstituted alkenes. Cross-selectivity is achieved by exploiting the ambiphilicity of organoboranes and fine-tuning their propensity to act as nucleophiles through transmetalation or as electrophiles in the formation of boron-ate complexes. Mechanistic studies reveal an unprecedented sequence of anti-selective carbometalation and anti-selective β-hydride elimination that results in stereospecific alkene formation, establishing a new mode of catalytic cross coupling.